Bosch Rexroth Rineer - GRINDING BASICS

Report
GRINDING BASICS
Presented by Dale Savington
For:
Bosch Rexroth – Rineer Hydraulics
• Cylindrical Grinding Processes
• Machine Requirements (Utilizing CBN)
• Abrasives
• Properties of Abrasives
• Superabrasives
• Bonds
• Mechanics of Grinding
• Coolant
• Truing & Dressing
CYLINDRICAL
PROCESSES
(GRINDING BETWEEN CENTERS)
Conventional
Plunge / Face Grinding
• Down-Feed (face bump grind)
• Q’ (Prime) 2.14 (0.2) +
• Wheel Velocity
• S.F.P.M. 8,500 +
• m/sec. 43 +
• High volume of coolant to get into grinding zone
Conventional
Traverse Grinding
• Cross –Feed (Traverse) only
• Stock Removal (in-feed depth)
• 0.0” to 0.0178 mm (0.0007”)
• ≥ 10% of abrasive Ø / pass
• Traverse rate
•10 – 25% of wheel width per
rotation of part
• Wheel Velocity
• S.F.P.M. 8,500 +
• m/sec. 43 +
• Finish Grinding
Peel (“Quick Point”) Grinding
• Multiple grinding functions
Wheel face configuration
• Wheel Velocity
• S.F.P.M. 17,000 +
• m/sec. 86 +
• Easier coolant delivery into grinding zone (narrow contact area)

Cylindrical Grinding Plunge

Q Prime (Q’) = work
piece diameter
x 3.14
(π) x in-feed rate
Example:
Work piece diameter = 25.4mm (1”)
In-feed rate = 4.039mm/min. (0.159”/minute)
Q’ then equals:
(25.4 x 3.14 x 4.039)/60 = 5.37 mm3/mm· sec.
1 x 3.14 x 0.159 = 0.5 in3/in· min.
Therefore:
(5.37/(3.14 x 25.4)) x 60 = 4.039mm/min.
0.5/(3.14 x 1”)= 0.159”/min. infeed rate
Note: (mm3/mm· sec.) to (in3/in· min.) conversion of 10.75
Surface Grinding
CONVENTIONAL
GRINDING
Wheel Speed = S l o w
Stock Removal = Light
Fast
CREEP FEED
Wheel Speed = S l o w
Stock Removal = Heavy
Slow
HEDG
(HIGH EFFICIENT DEEP GRINDING)
Wheel Speed = Fast
Stock Removal = Heavy
Fast

Surface Grinding

Q Prime (Q’) =In-feed
rate/pass x Traverse rate/min.
Example:
In-Feed per pass= 0.0508mm (0.002”)
Traverse rate per min.= 3,810mm (3.81m)/min. (150” (12.5’)/minute)
Q’ then equals:
(0.0508 x 3,810)/60 = 3.225 mm3/mm· sec.
0.002 x 150 = 0.3 in3/in· min.
Therefore:
(3.225/(0.0508) x 60 = 3,810mm/min. traverse rate
0.3/(0.002”)= 150”/min. traverse rate
Note: (mm3/mm· sec.) to (in3/in· min.) conversion of 10.75
MACHINE
REQUIREMENTS
MACHINE RIGIDITY
Spindle’s
Slides
Centers
Head Stock
Tail Stock
Base
Parts will Mirror Machines Rigidity
Wheel Spindle POWER!
Kilowatts!
Wheel spindle power per 25.4mm (1”) of wheel to work contact
Conventional Abrasives = 3.75 Kw (5 H.P.)
CBN Abrasives = 7.5 Kw (10 H.P.)
(HEDG) = 18.75 Kw (25 H.P.)
Peel – depends on contact area, material and stock removal
SPINDLE INTEGRITY
Run-Out
Out of Balance
Static Balance
Dynamic Balance – real time
WHEEL BALANCE
(DYNAMIC VS STATIC)
Portable Dynamic Balance

Static Balance allows balance in stationary position off the spindle.

Dynamic Balance is continuous balance on the spindle at working
rotating speeds.
WHEEL BALANCE
(DYNAMIC VS STATIC)
Dressing:

Sound of dresser touching wheel through
coolant.

Complete contact = dressed wheel
Other uses:

Picture of grinding process

Crash prevention
ACOUSTIC SENSORS
MACHINE REQUIREMENTS
(MAXIMIZING GRINDING PROCESS)
Rigidity
Coolant Flow
Spindle power
Smooth Transitional Plumbing
Wheel Velocity
Coolant Tank Capacity
Rotary Dresser
Coolant with lubricity
Acoustic Sensors
Dynamic Balancing
ABRASIVES
WHAT AFFECTS ABRASIVE DECISION?
Ferrous Materials
Non-Ferrous Materials
Fatigue Concerns
(Potential thermal damage)
Production Numbers
Dimensional Tolerances
Process Controls
TYPES OF ABRASIVES
Aluminum Oxide
Silicon Carbide
Cubic Boron Nitride (CBN)
Diamond
ABRASIVE SELECTION
Ferrous Materials
Non-Ferrous Materials
Cubic Boron Nitride (CBN)
Diamond
Aluminum Oxide
Silicon Carbide
PROPERTIES OF
ABRASIVES
ALUMINUM OXIDE
(AL2O3)
For Grinding
Ferrous Materials
Thermal Conductivity
O
(W/m K) = 29
Hardness on Knoop Scale
(kg/mm2) = 1400 - 2100
SILICON CARBIDE
(SI,C)
For Grinding
Non-Ferrous Materials
Hardness on Knoop Scale
(kg/mm2) = 2700
Thermal Conductivity
O
(W/m K) = 400
CUBIC BORON NITRIDE (CBN)
(B,N)
For Grinding
Ferrous Materials
Hardness on Knoop Scale
(kg/mm2) = 4500
Thermal Conductivity
O
(W/m K) = 1300
DIAMOND
(C)
For Grinding
Non-Ferrous Materials
Hardness on Knoop Scale
(kg/mm2) = 8000
Thermal Conductivity
O
(W/m K) = 2000
REVIEW
Knoop
Hardness
Aluminum Oxide
Silicon Carbide
Thermal
Conductivity
1400-2100
29
2700
400
Cubic Boron Nitride (CBN) 4500
1300
Diamond
2000
8000
THE PUZZLE
WHY NOT DIAMOND?
Diamond + Ferrous Material + Heat =
Note: Silicon Carbide has similar reaction
SUPERABRASIVES
WHAT ARE SUPERABRASIVES?
Diamond
Cubic Boron Nitride (CBN) Borazon

WHAT MAKES SUPERABRASIVES SUPER?
Hardness - (Resistance to wear)
Thermal Conductivity- (The ability to absorb heat)
Flexibility- (one wheel for many applications)
Wheel Life- (100 + times Conventional Abrasives)
SOME ADVANTAGES
(FOR SUPERABRASIVES)
Decreased Cycle Time
Reduced Dressing
Reduced Gaging
More Consistent Parts (Less Scrap)
Reduced Time for Wheel Changes
Reduced Coolant Changes
Reduced Filter Changes
Reduced Coolant Disposal Costs
Less Swarf Contamination
CONVENTIONAL ABRASIVES
CONSTRUCTION
Conventional Layer = full area of wheel
Wheel
Vitrified Bond
Resin Bond
Rubber Bond
Shellac Bond
SUPERABRASIVE CONSTRUCTION
Superabrasive Layer = 3mm (1/8”) to 12.7mm (1/2”)
Wheel
Core
Resin Bond
Metal Bond
Vitrified Bond
BONDS
GRINDING MATRIX
VITRIFIED WHEEL
Grain
Pore
Bond
Chip
GRINDING WHEEL
BOND SYSTEMS
Resin , Metal &
Bonds
Abrasive + Bond = Wheel
GRINDING WHEEL
BOND SYSTEMS
Open Structure (Low fired) Vitrified Bonds
Abrasive + Bond + Pores = Wheel
GRINDING WHEEL
BOND SYSTEMS
Plated Wheels (Single Layer)
Wheel body
Cathode (-)
Abrasive
Anode (+)
Electrolyte
(Nickle Solution)
Plated Wheel
Cut-A-Way
Mechanics of Grinding
ABRASIVE WEAR
Bond
Abrasive
Fracture wear
Chip
Cut a way of wheel
Conventional
Abrasive (one grain)
Attritious wear
(Rubbing)
ABRASIVE WEAR
Work Piece
Conventional
Abrasive (one grain)
Fracture wear
Work Piece
ABRASIVE WEAR
Conventional
Abrasive (one grain)
Fracture wear
Work Piece
ABRASIVE WEAR
CBN
Abrasive (one grain)
Attritious wear
Work Piece
ABRASIVE WEAR
STANDARD MARKINGS
CONVENTIONAL ABRASIVES
Abrasive
Type
Abrasive
Size
A
C
SG30
60
120
80
A
24
Abrasive
(combination)
1
2
Hardness
(Grade)
Structure
(Pore)
Bond
J
K
L
6
12
10
V
V
V
R
B
STANDARD MARKINGS
SUPERABRASIVES
Abrasive Type
Abrasive Size
Hardness
(Grade)
Concentration
Bond
BN
D
BN
140
240
120
J
k
L
100
75
150
B
M
V
Superabrasives are always combinations 120/140, 80/100 etc.
Calculating concentration take number and divide by 4
Example 100 ÷ 4 = 25% by volume of abrasive in wheel
COOLANT
Type, Flow, Pressure & Nozzle Design
COOLANT TYPES
Water, Water Soluble Oils, Straight Oils
Specific Gravity of each & traits for grinding:
Water = 1 SG (Issue – lack of Lubricity)
Water Soluble Oil = 1 SG (Issues – Foaming & bacteria)
Straight & Synthetic Oils = 0.87-0.95 SG (Issues – Heat & Disposal)
( Specific Gravity (SG not a factor in calculations) )
COOLANT CONDITION
Tank Size &
Coolant Temp.
Filtration &
Particle Distribution
Chemistry
(Lubricity)
COOLANT PRESSURE
Equal Wheel Velocity
Bernoulli’s Equation for Pressure
ΔP (Bar) = SG x Vj2 / 200
Where:Vj2 = (M/s)2
Example: Wheel velocity – 43.3M/s (8,500 S.F.P.M.)
Then: 1 x (43.3)2 / 200 = 9.4 Bar
Bar conversion Bar x 14.508 = 136 psi
Bernoulli’s Equations
Bernoulli's Equation: P = SG x Vj2 / 535824
Where: P = psi
Vj = (S.F.P.M.)2
SG = Specific Gravity of coolant
135 psi
Metric Pressure (Bar)
Bernoulli's Equation: ΔP = SG x Vj2 / 200
Where: ΔP = Bar
9.4 bar
Vj2 = (M/s)2
SG = Specific Gravity of coolant
Inch Velocity - (S.F.P.M.)
Bernoulli's Equation: Vj = (19.25 x Q) / Aj
Where: Vj = Velocity (S.F.P.M.)
8,075 S.F.P.M.
Q = Flow rate (G.P.M.)
Aj = Area of nozzle exit (in2)
Metric Velocity - (M/s)
Bernoulli's Equation: Vj = (103 / 60) x (Q/Aj)
Where: Vj = Velocity (M/s)
Q = Flow rate (Liters/min.)
Aj = Exit area of nozzle exit (mm2)
Inch aperture size - (In2)
Bernoulli's Equation: A j= (19.25 x Q) / (CD x Vj)
Where: Aj = aperture (in2)
Q = GPM
CD = 0.95
Vj = Velocity (S.F.P.M.)
Metric aperture size - (mm 2)
Bernoulli's Equation: Aj = (10^3 x Q) / (Vj x 60)
Where: Aj = aperture (mm2)
Q = LPM
CD =0.95
Vj = Velocity (M/s)
41 M/s
2
0.03142 in
19.4 mm2
Coherent-Jet Nozzle Calculator (Dr. John Webster)
Inch
Metric
INPUT
Coolant
Jet
Specific Speed
Gravity Required
SG
SFPM
1
8,500
OUTPUT
Nozzle
Exit
Diameter
inch
0.2
psi
GPM
pounds
Coolant
Specific
Gravity
SG
135
13
8
1
Pressure
Flowrate
at Nozzle
Calculated GPM per H.P. Used / area
Spindle H.P. (Max)
25
Conv. wheels
Spindle H.P. no load
Spindle H.P. full load
4
10
Some specific gravities (SG)
Type of Coolant
SG at 20°C
Mineral oil
Synth oil
Water
0.87
0.95
1
Area for Rectangular Nozzle
Length
Height
Area
Metric Conversion of above #'s
INPUT
CBN wheels
Reaction
Force
GPM
12
43
Spindle Kw no load
Spindle Kw full load
GPM
12
27
48
75
109
193
inch
0.622
0.824
1.049
1.380
1.610
2.067
5.10
Pressure
Flowrate
at Nozzle
Pipesize
schedule
40
inch
1/2
3/4
1
1-1/4
1-1/2
2
3
7.3
Some specific gravities (SG)
Type of Coolant
SG at 20°C
Mineral oil
Synth oil
Water
0.87
0.95
1
LPM
Newton
9.4
50.4
36.4
Round
Length
LPM
43.0
CBN wheels
34.4
Flowrate
ID of
Pipe
Pipesize
schedule 40
L/min
50
100
180
300
400
750
mm
16
21
27
35
41
53
inch
1/2
3/4
1
1-1/4
1-1/2
2
Calculated Area of nozzle exit
in2
mm 2
0.03142
20.428
0.200
Reaction
Force
bar
Calculated LPM per Kw Used / area
Spindle Kw (Max)
18.4
Conv. wheels
9
Max.
ID of Pipe
Flowrate
OUTPUT
Jet
Nozzle
Speed
Exit
Required Diameter
M/s
mm
5.1
Note: The above results are for a given area. If you have multiple nozzles then if all have the same dimension the
GPM or LPM must be multiplied by the number of nozzles to obtain correct needed flow rate.
Copyright © 2013 [Dale Savington]. All Rights Reserved
Coolant Flow Calculations
Coolant Type
mm or Inch
Water Soluble
drop down box
mm
drop down box
Average if Multiple Nozzles of Height of Nozzle Openings
Average if Multiple Nozzles Contact of wheel to Part length (Nozzle Length)
Average Nozzle Diameters
# of Round Nozzles
Height
Length
5.100
3
# of Rectangular Nozzles
Diameter
# of round nozzles
# rectangular nozzles
Grinding Wheel Rotation
1,600
Grinding Wheel Diameter
508.000
Wheel rpm
Wheel Diameter
Velocity % Coolant (Faster Than Wheel Velocity)
Calculated Coolant Flow rate Needed
Calculated Coolant Pressure Needed
41
131
Actual Measured Coolant Pressure
131
Pressure (P.S.I.)
9.0 Bar
Actual Measured Coolant Flow rate
Gallons Per Minute
% of needed GPM
155 LPM
Measured Coolant Flow Percent Compared to Calculated Velocity Needed (GPM)
41
99%
Measured Coolant Pressure Compared to Calculated Pressure Needed (psi)
100%
% of needed P.S.I.
43
Gallons Per Minute
Pressure (P.S.I.)
Calculated M/s- Velocity
IMPORTANT: The calculated data is for optimum flow and pressure based on the nozzle geometry and numbers you have entered. However,
you will need to be sure that the actual measured pressure and flow rate are reflective of the calculated numbers. Mechanical realities such
as head loss, pump type, flow of coolant from pump etc will influence actual measurements.
Optimal measurements would be Pressure Gage and Flow Meter located at Manifold
156 LPM
9.0 Bar
Copyright © 2013 [Dale Savington]. All Rights Reserved
Conversion Table
Input
Conversions
mm:
Inch
Bar:
PSI
Meters per Second (M/Sec.):
Liters per Minute (LPM):
Pounds per Square Inch (PSI):
Head loss per foot (0.3048 meters):
Meters:
Wheel SFPM (Note: 164 minimum needed to register):
Power (Kw):
Gallons Per Minute (GPM) Formulation
Pressure Per Square inch (P.S.I.) Formulation
Note:
S.F.P.M.
GPM
Feed of Head
Nozzle PSI Loss
Feet
Nozzle PSI needed
H.P.
Nozzle Height x Wheel S.F.P.M. x 12
(231 ÷ Wheel "P" Line)
(Surface Feet Per Second (S.F.P.S.) of Wheel ÷ 12.2) 2
231 = in3/gal of H2O at Sea level (Standard Factor)
For PSI a factor of 0.87 is multiplied for Oil
"P" line of wheel equals the linear width of wheel
COOLANT FLOW
Rim Section
Grinding Wheel
Grinding Wheel
Grinding
Wheel “P”
Line
Work Piece
Work Piece
(Part) “P”
Line
Work Piece
“P” LINE /RIM SECTION
TRUING & DRESSING
THE DIFFERENCE BETWEEN
TRUING & DRESSING
TRUING
RESIN & METAL BONDS
DRESSING
RESIN & METAL BONDS
TRUING & DRESSING
PLATED WHEELS
TRUING & DRESSING VITRIFIED BONDED
(CBN WHEELS)
EXAMPLES OF ROTARY DRESSERS
Direction for Dressing with rotary Dressers
Preferred (opens wheel)
Closes Wheel

Conventional Abrasives – Aluminum Oxide


Ceramic Abrasives – Seeded Gel (SG)


≤ 0.0178mm (0.0007”) per pass
≤ 0.005mm (0.0002”) per pass
CBN Abrasives

≤ 0.0025mm (0.0001”) per pass
TRUING & DRESSING
(DEPTH OR IN-FEED)
TRUING & DRESSING
(TRAVERSE RATE)

Starting Parameters

0.1mm (0.004”) per revolution of wheel
Assuming 0.5mm (0.020”) radius dresser
Faster traverse rate creates rougher finish
Slower traverse rate creates finer finish
 Conventional
 CBN
Grinding Surface Finish = Grit Size
Grinding: Surface Finish = Diamond Overlap
CBN VS CONVENTIONAL
(SURFACE FINISH – PLUNGE
GRINDING ONLY)
Nozzle increased production by 42% (762mm/min to >1,065mm/min.) + decrease dress amounts.
“Automotive Valve Seats”
508mm x 458mm x 304.8mm
Vitrified CBN wheel
Thru-Feed Grinding
Metal bond rotary dresser
Dr. Webster Nozzle
Each orifice is an oval 4mm
19 total orifices
Hard Tuning Shafts to see if it was cost affective
Cost was prohibitive because of tool life and change times
the end

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